The present invention relates to an access control system of an actuator for fast positioning of an actuator which carries a plurality of magnetic heads in a magnetic disk storage/memory system.
In a large capacity magnetic disk storage for an on-line system, throughput must be increased so that the larger storage capacity of the hardware is used effectively.
A multi-actuator has a plurality of actuators each of which independently carries magnetic heads so that the storage for each actuator is reduced by divided actuators, and results in high speed access. Therefore, a multi-actuator considerably increases the throughput of the system.
However, a multi-actuator has a problem in that mechanical power applied to an active actuator is undesirably transferred to an adjacent actuator through mechanical parts of a head disk assembly, and disturbs the accurate tacking in the adjacent actuator. That disturbance would break the positioning of the adjacent actuator and cause a positioning error in adjacent actuators. Therefore, it is important to reduce the positioning error caused by interaction in an HDS (Head Disk Assembly) which employs a multi-actuator.
FIG. 18 shows a perspective view of a swing type multi-actuator which has two actuators. In the figure, the numeral 1 is an actuator, 2 is a pivot shaft, 3 is a magnet housing, and 4 is a sub-base support. The two actuators 1 are mechanically coupled with each other through the pivot shaft 2, the magnet housing 3, and the sub-base support 4. Therefore, mechanical vibration from one actuator is induced to another actuator through the mechanical coupling parts (pivot shaft, magnet housing, and sub-base support), and thus the transferred vibration can cause a positioning error of another actuator.
The above mechanical vibration has a frequency spectrum between several hundred Hz and several thousand Hz. Since the cutoff frequency in a servo loop for head positioning is usually several hundred Hz, which is less than one seventh of the mechanical resonance frequency of the actuator 1, the servo loop circuit can not make the actuator follow the transferred mechanical vibration, and therefore, the transferred undesired mechanical vibration directly causes a head positioning error.
A prior art for solving the above problem is to decrease the slewing rate (gradient) of the drive current in an actuator 1 so that the current has no spectrum close to the mechanical resonance frequency.
The prior art to decrease slewing rate has the advantages that the positioning servo loop is stable, and the circuit is simple.
However, the prior art has the disadvantages that the drive current or the power supply voltage must be large since the waveform of the drive current must be triangular in high velocity operation, and that the temperature of a head disk assembly is considerably increased due to large power consumption in a voice coil motor (VCM) and an amplifier which feeds current to the VCM.